Typhoid fever amongst other infectious diseases is still a serious public health concern in terms of severity and frequency of occurrence [1] [2] . The increased cost of conventional anti-typhoid drugs and an increase in resistance are making them to become more unavailable to patients in Africa [2] [3] . Typhoid fever is caused by Salmonella spp, a common intestinal pathogen that cause food poisoning and intestinal diseases [4] . Also, there is increasing global public health concern for humans and animals antimicrobial resistance by Salmonella species [5] . This situation has provided the impetus to the search for new antimicrobial substances from various sources including Schiff bases.

Schiff bases are compounds carrying an imine or azomethine (–C=N–) functional group prepared through a condensation reaction of primary amines and carbonyl containing compounds [6] [7] and have gained importance in present days as they are found to have a versatile pharmacophore for design and development of various bioactive lead compounds [8] . Vanillin (4-hydroxy-3-methoxybenzaldehyde) exhibits antimicrobial properties [9] . Moreover, Schiff bases derived from vanillin have been reported to have broad biological importance including antibacterial activity [10] . This provided the basis to study the antibacterial activity of Schiff bases derived from vanillin.

The melting points of the compounds were determined on a microprocessor melting point apparatus Zenithlab. The purity of all the compounds was routinely checked by TLC on Silica gel-GF 254 (Merck) coated plates. IR spectra were recorded on a Thermo Nicolet Nexus 670-FTIR. ¹³C NMR and¹H NMR spectra were recorded on a BrukerAvance III-HD operating at 150.90 MHz and 600.13 MHz respectively. Chemical shifts are reported in δ ppm using the internal standard TMS. All the solvents and chemicals used were of analytical grade. The biological activity of the synthesized compounds was determined by the disc diffusion method.

Synthesis of the Schiff base compounds

The compound (NT₁) was obtained by refluxing equimolar proportion of vanillin (0.152 g; 1.0 mmol) and nicotinic acidhydrazide (0.137 g; 1.0 mmol) in methanol (10 mL). The mixture was heated under reflux between 70˚C - 80˚C with continuous stirring for 8 hours. A pale yellow precipitate was filtered, washed with cold methanol and dried. The same procedure was used in preparing NT₂, NT₃ and NT₄ as represented in Scheme 1 using the amines shown on Table 1 below.

This work describes the synthesis of Schiff bases derived from vanillin. Four Schiff bases of vanillin with various aromatic amines (nicotinic acid hydrazide, 2, 4 DNPH, isoniazid and aniline) were synthesized and characterised by ¹³C NMR, ¹HNMR. The anti-salmonellal activity of the Schiff bases, amines and the aldehyde (vanillin) were bacteriostatic and in general relatively low. Condensation products (NT₁ - NT₄) are less active the vanillin (9) while compound NT₁, NT₂ and NT₃ were more active than their amines. These results rekindle the synthesis of more analogues especially those containing F, NO₂, -OCH₃. The Schiff base analogues will be complexed with selected transition metals and later screened for biological activities.

The authors are grateful to Professor Nfor Emmanuel of the department of Chemistrty, University of Buea. For supplying the amines used in the syntheses. Dr. Vincent de Paul Nzuwah Nziko of the Department of Chemistry and Biochemistry, Hampton University, Virginia is acknowledged for ¹H NMR data acquisition.